Towards ending the perioperative metformin controversy: a narrative review

Abstract

Metformin is the most widely prescribed oral glucose-lowering medication and serves as the first-line treatment for type 2 diabetes mellitus due to its efficacy, cost-effectiveness, and favourable safety profile. Given its widespread use, perioperative management of metformin is a common clinical challenge. Concerns regarding metformin and lactic acidosis have historically led to recommendations for its preoperative discontinuation. Recent studies, including randomized controlled trials, have found no significant difference in lactic acidosis risk between patients who continue or discontinue metformin perioperatively. However, these studies are highly heterogeneous, and the randomized controlled trials include a limited number of patients; on the other hand, metformin-induced and metformin-associated lactic acidosis are uncommon. We conducted an extensive narrative review of perioperative metformin guidelines, including ten publications from 2015 to 2024. Seven out of ten guidelines support continuing metformin in patients without risk factors, such as impaired renal function or the use of contrast agents. When risk factors are present, most guidelines recommend withholding metformin on the morning of surgery. There has been a notable shift in recommendations regarding resumption. Guidelines published before 2020 advised waiting 48 hours postoperatively, but more recent guidance suggests metformin can be restarted once adequate oral intake is established and renal function is confirmed to be stable. However, definitive large-scale randomized trials are still needed to establish standardized recommendations.